Recently, a virtual network using software and software defined networking (SDN), which is the technology of forming a virtual network, have attracted attention. In the SDN, a device called a controller manages a device included in a network. For example, a switch in the network transfers a received packet using a transfer rule acquired from the controller. When a packet which is not to be processed using a transfer rule is received, the switch notifies the controller of the information about the received packet, thereby acquiring from the controller the information for specification of the method of processing the packet. The switch performs the process of transferring the packet based on the information acquired from the controller. Thus, since the controller has an influence on the process performed by another device, it is designed to provide a plurality of controllers throughout a network to improve the fault tolerance and the extensibility of a system.
Designed as a related technology is a system including a plurality of controllers which calculate relative communication paths and a plurality of switches which relay a received packet through the path set by a path determiner in the plurality of controllers.
For example, a document such as Japanese Laid-open Patent Publication No. 2011-160363 etc. is well known.
There is a case in which a notification according to a transfer rule is not to be transmitted from a controller to a switch when a certain controller becomes faulty or when an excess load is applied to a certain controller although a plurality of controllers are included in a network. Even in such a case, a switch incapable of processing a received packet requests a controller to which the switch is connected for the information used in transferring the packet (that is, a transfer rule). In this case, since the switch requests the controller to transmit the transfer rule although the switch is not to acquire the transfer rule, the wasteful communicating process is performed, thereby decreasing efficiency.